1. Field of the Invention
This invention pertains, in general, to tooling which utilizes differential thermal expansion between fixture and workpiece components to impart a compressive load across a bond plane to affect a metallurgical bond.
2. Related Art
Costs for hot section nickel-based superalloy blades have increased as more sophisticated casting techniques and alloys, e.g., conventionally-cast, directionally-solidified and single crystal components, have been developed. Application of protective base coatings and thermal barrier coatings and the associated diffusion heat treatment schedules add to these costs.
Hot section components of gas turbines are subjected to severe service conditions, which include combinations of thermal and mechanical stresses that ultimately result in thermal mechanical fatigue cracking within the blade tip regions. For cost reasons, a method of repair or replacement of only the damaged tip segment, rather than replacement of the entire blade, is required. Damage blade tips are typically repaired using one of several weld procedures. Because of the difficulty in welding modern nickel-based superalloys, low strength, solid solution weld metal alloys are commonly used. However, the reduced mechanical properties of the weldment restrict repair to the lower stress regions of the blade. Other weld processes utilizing gamma prime strengthened filler materials at either ambient or elevated temperatures usually result in micro-fissuring of the weld metal and/or the heat affected zones. Further, costs associated with repairing one blade at a time are high.
Alternate bonding processes, e.g., diffusion welding, activated diffusion brazing, transient liquid phase bonding, have been developed which can produce near base metal properties. In addition to expanding the allowable repair regions of the blade, costs can be reduced significantly if bond tooling is developed which allows large batches of blades to be simultaneously repaired in conventional vacuum furnace systems. A requirement of this tooling would be the ability to apply hundreds of pounds per square inch to the bond planes of transient liquid phase bonds and thousands of pounds per square inch to the bond area of diffusion welded designs. Precise control of bond line loads is critical to the above-mentioned processes to achieve acceptable metallurgical quality.
Accordingly, it is an object of this invention to provide a low cost, high temperature tooling for transient liquid phase bonding or diffusion weld repair of gas turbine engine blade tips.
It is a further object of this invention to provide such high temperature tooling that can be employed to repair multiple blades at the same time in a batch process.
Additionally, it is an object of this invention to provide such high temperature tooling that can be employed to repair multiple blades of varying sizes in a batch process.